Stripe Rust Forecast and Update 3/13/14

March 13, 2014 – Xianming Chen

Prediction of potential stripe rust damage for the PNW

Using a series of forecast models (Sharma-Poudyal and Chen, Phytopathology 101:544-554, 2011) based on various weather parameters from November, 2013 to February, 2014 at Pullman, Washington, we predict a low level of stripe rust for the 2014 wheat crop season. The new prediction of potential yield loss on susceptible winter wheat varieties is 7.8±7.7%, decreased from the 22.3% forecasted based only on the December temperatures. This low level of stripe rust was not predicted or observed in the last decade for the Pacific Northwest (PNW). At such low level, most wheat varieties grown in the PNW may not need fungicide application. In comparison, last year we predicted yield loss on susceptible winter varieties as 44.0±3.5% and observed 42.4% yield loss in experimental fields. The prediction is based on historical yield loss and weather data of the Palouse region and is applicable for most wheat growing regions in the Pacific Northwest (PNW), except western Washington, western Oregon, and southern Idaho as these regions have quite different weather patterns. As always, the stripe rust pathogen should have survived the winter and started developing in the western PNW.

Yesterday, we were checking wheat fields along highway 26, 17 and 21 in Whitman, Adams, Franklin and Grant counties in Washington. Wheat plants ranged from Feekes 1 to 5, and in general survived this cold winter very well, except one field in Adams County appearing to have winter injure. We particularly checked the wheat field severely rusted in the last November and nearby fields out of Coulee City in Grant County, and did not found rust. In that particular field, old leaves were dead, but plants mostly survived.

Stripe rust in other regions

So far, stripe rust has been reported only in Texas. On March 4, stripe rust up to 30% severity or incidence was observed on some lines in an experimental field near Castroville, TX. Although this time of observation is latter than the first report of stripe rust in the region last year, any observation before April in south-central states is considered early and likely indicates significant stripe rust epidemic in the Great Plains and the eastern states. How quickly and widely will the pathogen spread and how severe will the disease develop will depend upon the weather conditions (temperature, moisture and storms) in the region and further north and east. Based on the general weather conditions so far and forecasted for March-May (warmer than average in southern Great Plains and average in central Great Plains; and average precipitation for most Great Plains), stripe rust will likely to have a limited and localized distribution this year. Growers in southern states should start to check their wheat fields and consider use of fungicides when stripe rust is found..